Carboxyl-Terminal Domain (CTD) of RNA polymerase II plays a number of roles. Which of the following is correct?

Question

BlackTom AI · Accepted Answer

To begin, let's consider what each statement claims about the Carboxyl-Terminal Domain (CTD) of RNA polymerase II and compare it against established features.
Option A: 'The CTD recognizes the promoter of genes and recruits transcription factors.' This is inaccurate. Promoter recognition and recruitment of general transcription factors occur at the promoter region through transcription factor proteins that bind DNA and assemble the pre-initiation complex, not primarily through the CTD. The CTD becomes important after transcription initiation for coordinating RNA processing processes, not for promoter recognition.
Option B: 'The CTD is required for recruiting the splicing machinery but not for capping.' This is misleading. The CTD coordinates multiple RNA processing events during transcription, including capping, splicing, and 3' end processing. It is involved in recruiting the cap-binding complex at the 5' end early in transcription and also helps recruit splicing factors as elongation proceeds. Saying it is not involved in capping ignores a well-established role of the CTD in capping factor recruitment.
Option C: 'The CTD recruits RNA processing machinery to the nascent transcript.' This reflects a core and well-supported function of the CTD. As RNA polymerase II transcribes a gene, the CTD serves as a scaffold that recruits capping enzymes, splicing factors, and 3' end processing factors to the growing transcript, facilitating co-transcriptional RNA processing.
Option D: 'The CTD contains a 7-nucleotide repeat which can be phosphorylated or methylated.' This is close but inaccurate in specifics. The CTD contains a repeating heptapeptide, not a 7-nucleotide repeat, and its regulation is primarily via phosphorylation (on serine residues) rather than methylation; thus this statement misstates both the nature of the repeat and the post-translational modifications.
In summary, Option C best aligns with the established role of the CTD in coordinating RNA processing machinery to the nascent transcript, whereas the other options describe incorrect or incomplete aspects of CTD function and structure.

Carboxyl-Terminal Domain (CTD) of RNA polymerase II plays a number of roles. Which of the following is correct?单项选择题

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